Bottlebrush or paperbark? Callistemon or Melaleuca?

This question arose from a somewhat cryptic sentence in the gardening column of our local newspaper, “The Tinaroo Bottlebrush (Melaleuca recurva but still sold as Callistemon recurvis) is a personal favourite…”

The question, of course, was, “Isn’t a Melaleuca a paperbark?” or words to that effect. A bit of digging (no, not in the garden) revealed the answers to a whole series of interconnected questions.

We’re dealing with two kinds of names of names for plants, common names and scientific (Latin) names, and both are problematic. The plants, however, are just as beautiful to us, and to the birds and butterflies, whatever they are called.

Scientific names

Scientific names are more precise than common names but they are sometimes changed by the taxonomists and these changes take time to percolate through to the rest of the scientific community and the general public. In this case we had two closely related groups of plants long classified in two genera, Callistemon and Melaleuca, recently merged under a single name. Callistemon [species name] therefore became Melaleuca [species name] overnight.

Angus Stewart of Garden Drum explains it pretty well:

I will find it hard to get used to saying Melaleuca as the new name for some of my favourite Australian plants such as ‘Captain Cook’, ‘Endeavour’ and ‘King’s Park Special’. But this is what it might come to if the botanical and horticultural world accepts a concerted push in the world of Australian botany to merge the genus Callistemon with its close relative Melaleuca.

The argument is that the differences between the two groups are insufficient for them to be kept separate. The rationale is explained in this excellent article on the website of the Australian Native Plants Society (Australia).

And we might as well follow him to ANPSA:

…the problem with the current classification on the basis of the arrangement of the stamens is that this supposed difference is not clear cut and Callistemon tends to merge into Melaleuca rather than being unambiguously distinct. The well known Callistemon viminalis is one that has often been discussed as not easily fitting the accepted definition of Callistemon.

Over the years there have been suggestions that the differences between species of the two genera are not sufficient to warrant them being kept distinct. A paper by Lyn Craven of the Australian National Herbarium (Novon 16 468-475; December 2006 “New Combinations in Melaleuca for Australian Species of Callistemon (Myrtaceae)”) argues that the differences between the two genera are insufficient to warrant them being retained separately and that they should be combined. As Melaleuca has precedence, adoption of Craven’s work would transfer all species of Callistemon into Melaleuca. Some state herbaria have adopted this change but, at this stage, the re-classification has not been taken up in the Australian Plant Census, which ANPSA recognises as the authority on plant nomenclature. For this reason we have retained Callistemon and Melaleuca as separate genera.

While all Callistemons have their flowers arranged in a “bottlebrush” shape the inflorescences of Melaleuca may also have a globular or irregular shape. It should also be remembered that there are other genera in the myrtle family which may have free or united stamens combined with “bottlebrush” flowers. Botany was never meant to be easy!

So the debate began more than ten years ago and isn’t over yet although the result seems clear enough.

One last little wrinkle is that the form of the species name must match that of the genus, which is why Callistemon recurvis became Melaleuca recurva rather than M. recurvis.

Common names

Staying with ANPSA for a moment longer:

…only Callistemons are commonly called “Bottlebrushes” ; Melaleucas are usually called “Paperbarks” or “Honey Myrtles” or sometimes “Tea Trees” although that name is more appropriate to another related genus, Leptospermum.

Paperbarks are named for their bark and bottlebrushes for their flowers. Given that some bottlebrushes have papery bark and some paperbarks have bottlebrushy flowers (sorry, but it’s hard to be more serious), the separation of common names must always have been blurred.

In fact, one particular tree in our own garden has been worrying me for years on just this account. We have two small trees which are unambiguously bottlebrushes (one is a hybrid, but let’s not go there), one huge tree which is unambiguously a paperbark, and a tall but very scrawny tree with papery bark and red bottlebrush flowers:

Is it a paperbark or a bottlebrush? Either or both, since common names are like that. Melaleuca or Callistemon? It’s now a Melaleuca, whatever it used to be.

Just for the sake of completeness

• Banksias also have bottlebrush-shaped flower spikes but are distinctive enough not to be easily confused with Melaleucas.
• Grevilleas are more closely related to Banksias than to Melaleucas but some have flowers which might mislead the casual onlooker. The common name of large species is “Silky Oak” but most species are known, like Banksias, by their Latin name.
• Leptospermums are in the same family as Melaleucas (Myrtaceae) and share their common name, “Tea Tree”, with paperbarks.
• “Tea tree” is sometimes also spelt “ti-tree”.
• Tea tree oil is extracted from a Melaleuca.